The present invention is directed to a novel bipolar cooling plate, fuel cell design and assembly. In particular, the present invention is directed to a fuel cell design which enables pretesting of a short stack of fuel cells (i.e., building blocks) prior to assembly into a tall multi-cell fuel cell stack. This novel design makes dismantling of the tall multi-cell fuel cell stacks easier and safer.
Fuel cells can be extremely advantageous as power sources, particularly for certain applications, such as a primary source of power in remote areas with limited access to convential power sources. It is of course necessary in these instances that the power system not only be self contained, but extremely reliable.
In the past, various fuel cell designs have been devised to accomplish these purposes. A typical fuel cell is comprised of a matrix material for holding electrolyte and an electrode disposed on each side of the matrix and in contact therewith. Reactant gases are fed to the nonelectrolyte side of each electrode. In a stack of fuel cells gas impervious separator plates are disposed between adjacent cells. The cells convert the reactants, such as hydrogen and air (i.e. O.sub.2) into D.C. electrical power in a manner well known in the art. The electrochemical reaction produces, as a by-product, waste heat which must be removed in a controlled manner to maintain the cells at the desired operating temperature. For the most efficient operation it is desirable to maintain all cells at a uniform temperature and at a maximum level consistent with material compatability characteristics.
In current practice, tall stacks of many individual fuel cells connected in series are formed to produce a cell having a practical voltage. For example, the voltage of a single fuel cell is usually in the order of a half volt. Accordingly, if 200 one-half volt cells are piled into a stack the electric potential of the stack would be approximately 100 volts.
In assembling the tall fuel cell stack individual cells are formed first. Each individual cell resembles a sandwich structure comprising a bipolar plate, an anode, a matrix and a cathode. The individual cells are piled up, and the stack is compressed by an externally applied load to assure intimate electrical contact of the components and gas tight sealing of the surfaces. This compression is an essential part of the assembly procedure. Once the fuel cell stack is compressed, phosphoric acid (electrolyte) can be added to the dry matrices without fear that the acid will leak out from the layers of the sandwich structure. The fuel cell stack becomes functional only after the acid is added. That is, the cell is now capable of generating electric current provided an appropriate fuel such as H.sub.2 and O.sub.2 is passed through the cell interior.
While the above described assembly procedure appears good in theory, there are many practical manufacturing problems associated with it. The major problem is that the tall fuel stack can only be tested after it has been assembled and filled with acid. The likelihood of each individual cell of the stack performing within the specified limit is extremely poor. Accordingly, in the case of a failure, as for example an open circuit, the stack must be dismantled and the faulty cell removed and replaced. Obviously, this is a hazardous and cumbersome procedure because the cells are now filled with concentrated phosphoric acid. In addition, the reassembly of the stack is just as dangerous and difficult with no guarantee that everything will be functioning after reassembly. Accordingly, a second or third iteration may be required before the stack performs as specified. Finally, other problems can develop once the stack is in operation. For example, seals separating the fuel from the oxygen or phosphoric acid from the gas reactant can develop leaks. If this occurs, dismantling and reassembly is again required.
From the aforementioned discussion, it is readily apparent that there is a need to pretest the fuel cells prior to assembly into tall stacks. This pretesting would eliminate malfunctioning cells prior to final assembly. It is with this object in mind that the novel fuel cell design and assembly of the present invention have been developed.